Ablation, such as ablation using a catheter, is a minimally invasive procedure. In this procedure, cardiac tissue is locally affected in order to block undesired conduction pathways. This can be achieved by hyperthermia using e.g. radio frequency (RF) as energy source. Upon energy delivery, a lesion starts to grow through the depth of the tissue wall, which becomes non-conducting scar tissue. Electrophysiologists aim to create lesions that run completely through the tissue wall (i.e. transmural) and are permanent (i.e. coagulated tissue, no recovery possible).
Tissue ablation is not without risk. One or more bubbles may form in the tissue during ablation, and rapid release of bubble energy can be induced.
If the tissue temperature rises rapidly, intramural evaporation may occur and a gas bubble may develop within the tissue under the electrode. Continuous application of RF energy will cause the bubble to expand and its pressure to increase, which may lead to eruption of the gas bubble through the weakest path, leaving behind a gaping hole. The release of the gas bubble is associated with a popping sound and, likely, with tearing of cardiac tissue.
In the following, such rapid release of bubble energy is referred to as a so-called “pop” or a “tissue pop”. This is associated with severe complications, such as tamponades in case of cardiac ablation, and clinicians try to avoid formation of such pops.
The reference ‘Detection of microbubble formation during radiofrequency ablation using phonocardiography’, published in Europace (2006), 8, 333-335, discloses that characteristic acoustic signatures are present before pops and correspond to microbubble (MB) formation. However, the ability to record acoustic sounds of MB formation in vivo is not known and may be complicated by respiratory, cardiac, and muscle artefacts.
Hence, there is the need for a solution that overcomes the aforementioned disadvantages and provides a safer ablation process; this would prevent injury during ablation procedures.